In general, the application of an air bag for restraining a rider in the event that an impact greater in level than a predetermined value is applied to a vehicle body of a motorcycle is known.
For example, it has been known to provide a vehicle with a substantially rectangular-shaped air bag module integrally containing therein a folded air bag and an inflator for inflating and developing the air bag and the like having a configuration in which the surface(s) of an air bag module cover as a predetermined development surface(s) is provided with a tear line as a brittle portion. Accordingly, at the time of inflation and development of the air bag, the pressure inside the air bag is raised by a gas generated from the inflator, whereby the tear line is ruptured and the air bag is developed. The tear line is required to have such a brittleness as to be appropriately ruptured at the time of inflation and development of the air bag and, simultaneously, to have such an appropriate strength as not to be deformed or ruptured when touched by the rider (passenger) or the like.
For example, Japanese Patent Laid-open No. 2005-162033 discloses such a configuration of an air bag module cover for application to a passenger seat air bag system in a four-wheel vehicle, wherein a tear line formed across a development surface(s) is in the shape of a single arc. According to this air bag module cover, even when the tear line and the surrounding portion are pushed by the passenger or the like, the pushing force is dispersed to the arc-shaped peripheral portions, so that the tear line and the surrounding portion are enhanced in rigidity and are less liable to be depressed. Also, both end portions of the first tear line are orthogonally intersecting with rectilinear second tear lines, so that, at the time of inflation and development of the air bag, the force exerted on the tear line is transmitted evenly, and smooth development of the air bag is realized.
Also, Japanese Patent Laid-open No. 2003-212075 discloses an example of a tear line structure formed in an air bag module cover for a four-wheel vehicle air bag system. In this tear line structure, an anti-leaking member provided for preventing a foamable resin of a foamable resin layer from flowing from a development portion into the air bag side, at the time of forming a perforation having a predetermined depth from the back side of the air bag module cover by laser processing, is removed only at the portion on the tear line, so that non-evenness of rupture of the tear line due to the anti-leaking member is obviated, and smooth development of the air bag is realized.